UM1755 Datasheet, PDF (7/123 Pages) STMicroelectronics – The purpose of this document is to describe the design of the application

UM1755
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Overview
Overview
Bluetooth LE technology was adopted by the Bluetooth SIG starting from the Bluetooth core
specification v4.0. Bluetooth LE technology was designed to enable products that require
lower power consumption, lower complexity and lower cost compared to the Bluetooth
classic or Bluetooth high-speed systems.
A typical BLE system consists of an LE controller and a host. The LE controller consists of a
physical layer (PHY) including the radio, a link layer (LL) and a standard host controller
interface (HCI). The host consists of a HCI and other higher protocol layers, e.g. L2CAP,
SM, ATT/GATT, GAP etc.
In many designs the LE controller and the host reside in two separate silicon chips and are
controlled by 2 different microcontrollers. Communication between the two is transmitted via
a hardware connection, e.g. UART, SPI, USB, etc. The host can send HCI commands to
control the LE controller. The HCI interface and the HCI commands are standardized by the
Bluetooth core specification. Please refer to the official document for more information.
The HCI interface provides a significant benefit. Any Bluetooth tester can easily connect to
the controller via the hardware connection, e.g. SPI, to test the controller by sending HCI
commands. This removes the need to involve the host if the only interest is to test the
controller.
Figure 1. Bluetooth LE system with separate host and controller
Sometimes the LE controller and the host can be combined into a single chipset solution.
This lowers the cost of hardware, first because it reduces the number of silicon chips to one
rather than two, and second because the hardware connection between the host and the
controller is no longer required.
Under this scenario, the host may directly control the LL/PHY. In this way, there is no need
to generate the standard HCI commands, transmit the commands to the LL, and then
process them. As a result, the execution time is improved and the calculation load on the
CPU is reduced. However, if the HCI is removed completely, it will be more difficult to test
only the controller with an external Bluetooth tester.
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